Method and device for making a metal bump with an increased height

ABSTRACT

A device for making metal bumps includes a hard conical tubular member having a vertical passage which is conical in shape and has a larger diameter at a bottom such that a lower portion of the vertical passage is larger than an upper portion of the vertical passage, whereby a metal wire is inserted into the vertical passage of the hard conical tubular member, with a lower end of the metal wire protruded downwardly out of the vertical passage, the lower end of the metal wire is melted to form a ball, the hard conical tubular member is approached to a raised platform formed on a top of a chip, and a load is applied to the metal wire and the metal wire is heated and bonded on the pad of die and ultrasonic energy is applied to deform the melted metal so as to fill up the lower portion of the vertical passage thereby forming a metal bump on the raised platform of the chip, and finally the hard conical tubular member is removed to pull off the necking position between the metal wire and a top of the metal bump thereby leaving the metal bump on the raised platform of the chip.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention is related to a method and device for making ametal bump with an increased height and in particular to one which canincrease the connection reliability between the metal bump and the chipand enlarging the contact area between the metal bump and the metal orsolder ball.

[0003] 2. Description of the Prior Art

[0004] Various kinds of methods of making metal bumps on a chip havebeen developed for flip chip on board (FCOB) technology with a smallnumber of input pins or a small number of Input/Output pins or for flipchip in package (FCIP) with a large number of Input/Output pins, such asevaporation plating, splash plating, electroplating, printing, spraying,and bonding. However, the capillary tube is still the most commonly usedtool for making metal bumps by means of wire bonding. The capillary tubehas an inner diameter with an inner wall and has a larger diameter atthe upper end than the lower end. A metal wire is inserted into thecapillary tube and the lower end of the metal wire is melted to form aball shaped member by electric spark. Then, ultrasonic vibration andpressure deformation processing are applied to the capillary tube tojoin the inter-metallic compounds between the wire and the chip. Whenthe capillary tube is removed, a metal bump will be formed on the raisedplatform of the chip. Thereafter, a metal or solder ball is soldered onthe metal bump.

[0005] However, due to the limitation of the design of the capillarytube, the metal bump will have a spherical surface which is insufficientto provide a large contact area and a reliable structure for joiningother component parts. Furthermore, the bottom of the metal bump willtend to go beyond the lower opening of the capillary tube under pressurethereby making it difficult to control. Moreover, as the metal bump hasa spherical surface, there will not be sufficient area in contact with ametal or solder ball. In addition, the metal bump is so short that themetal or solder ball must be soldered to the metal bump at a very lowposition thereby making it difficult to make the connection between thechip and the fingers of a substrate (or lead frame, chips, metal bumpsor the like) and therefore influencing the qualification rate ofproducts.

[0006] Therefore, it is an object of the present invention to provide amethod and device for making a metal bump with an increased height whichcan obviate and mitigate the above-mentioned drawbacks.

SUMMARY OF THE INVENTION

[0007] This invention is related to a method and device for making ametal bump with an increased height.

[0008] It is the primary object of the present invention to provide amethod and device for making metal bumps with an increased height whichcan increase the joining strength with other metal bumps or pads of adie.

[0009] It is another object of the present invention to provide a methodand device for making metal bumps with an increased height which canenlarge the contact area with the metal or solder ball.

[0010] It is still another object of the present invention to provide amethod and device for making metal bumps with an increased height whichcan increase its reliability in joining with other component parts.

[0011] It is a further object of the present invention to provide amethod and device for making metal bumps which have an increased heightbut are small in diameter.

[0012] The foregoing object and summary provide only a briefintroduction to the present invention. To fully appreciate these andother objects of the present invention as well as the invention itself,all of which will become apparent to those skilled in the art, thefollowing detailed description of the invention and the claims should beread in conjunction with the accompanying drawings. Throughout thespecification and drawings identical reference numerals refer toidentical or similar parts.

[0013] Many other advantages and features of the present invention willbecome manifest to those versed in the art upon making reference to thedetailed description and the accompanying sheets of drawings in which apreferred structural embodiment incorporating the principles of thepresent invention is shown by way of illustrative example.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a sectional view of a capillary tube according to thepresent invention;

[0015]FIG. 2A illustrates the lower end of a metal wire being melted toform a ball shaped member according to the present invention;

[0016]FIG. 2B illustrates how the lower end of the metal wire is joinedwith the chip according to the present invention;

[0017]FIG. 2C illustrates a metal bump according to the presentinvention;

[0018]FIGS. 3A and 3B illustrate the connection between the metal bumpand the metal or solder ball according to the present invention; and

[0019]FIGS. 4A and 4B illustrate the connection between the metal bumpand the metal or solder ball according to the prior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0020] For the purpose of promoting an understanding of the principlesof the invention, reference will now be made to the embodimentillustrated in the drawings. Specific language will be used to describesame. It will, nevertheless, be understood that no limitation of thescope of the invention is thereby intended, alterations and filtermodifications in the illustrated device, and further applications of theprinciples of the invention as illustrated herein being contemplated aswould normally occur to one skilled in the art to which the inventionrelates.

[0021] Referring to the drawings and in particular to FIG. 1 thereof,the metal bump according to the present invention is manufactured by ahard conical tubular member 20 having a vertical passage 21 which isconical in shape and has a larger diameter at the bottom 231 so that thelower portion 23 of the vertical passage 21 is larger than the upperportion 24 of the vertical passage 21. The vertical passage 21 has aninner surface 22.

[0022] Referring to FIGS. 2A, 2B and 2C, a metal wire 3 is inserted intothe vertical passage 21 of the hard conical tubular member 20, with itslower end protruded downwardly out of the vertical passage 21. Then, thelower end of the metal wire 3 is melted to form a ball 31. Thereafter,the hard conical tubular member 2 is approached to a raised platform 11formed on the top of a chip 1, and a load (not shown) is applied to themetal wire 3 and the metal wire 3 is heated and bonded on the pad of dieand ultrasonic energy is applied to deform the melted metal so as tofill up the lower portion 23 of the vertical passage 21, thereby forminga metal bump 32 on the raised platform 11 of the chip 1. Thereafter, thehard conical tubular member 2 is removed to pull off the neckingposition between the metal wire 3 and the top of the metal bump 32thereby leaving the metal bump 32 on the raised platform 11 of the chip1. As the bottom opening of the lower portion 23 of the vertical passage21 is formed with an angle 231, the metal bump 32 will be formed with aflange 321 at the bottom thereof (see FIG. 2B).

[0023] Accordingly, the metal bump 32 will have an increased height 232thereby increasing the joining capability between the metal bump 32 andthe raised platform 11 of the semiconductor chip 1 and enlarging thecontact area 33 between the metal bump 32 and the metal or solder ball4.

[0024] As the metal or solder ball 4 is joined to the metal bump 32 (seeFIGS. 3A and 3B), the metal or solder ball 4 will be pressed by asoldering finger 5 thereby deforming the shape of the metal or solderball 4 and therefore causing the deformed metal or solder ball 4 to gooutwardly. In the meantime, the flange 321 of the metal bump 32 willblock the metal or solder ball 4 to overflow to the raised platform 11of the chip 1. Referring to FIGS. 4A and 4B, according to the prior art,the metal or solder ball 4′ will be pressed by a soldering finger 5′when the metal or solder ball 4′ is joined to the metal bump 32′,thereby deforming the shape of the metal or solder ball 4′ and thereforecausing the deformed metal or solder ball 4′ to overflow to the raisedplatform 11′ of the chip 1′. Hence, the connection reliability betweenthe chip and the fingers of a substrate (or lead frame, chips, metalbumps or the like) will be decreased and therefore influencing thequalification rate of products.

[0025] It will be understood that each of the elements described above,or two or more together may also find a useful application in othertypes of methods differing from the type described above.

[0026] While certain novel features of this invention have been shownand described and are pointed out in the annexed claim, it is notintended to be limited to the details above, since it will be understoodthat various omissions, modifications, substitutions and changes in theforms and details of the device illustrated and in its operation can bemade by those skilled in the art without departing in any way from thespirit of the present invention.

We claim:
 1. A device for making metal bumps comprising a hard conicaltubular member having a vertical passage which is conical in shape andhas a larger diameter at a bottom such that a lower portion of saidvertical passage is larger than an upper portion of said verticalpassage, whereby a metal wire is inserted into said vertical passage ofsaid hard conical tubular member, with a lower end of said metal wireprotruded downwardly out of said vertical passage, said lower end ofsaid metal wire is melted to form a ball, said hard conical tubularmember is approached to a raised platform formed on a top of a chip, anda load is applied to said metal wire and said metal wire is heated andbonded on the pad of die and ultrasonic energy is applied to deform saidmelted metal so as to fill up said lower portion of said verticalpassage thereby forming a metal bump on said raised platform of saidchip, and finally said hard conical tubular member is removed to pulloff the necking position between said metal wire and a top of said metalbump thereby leaving said metal bump on said raised platform of saidchip.